The idea of this ticket is to support the following use case.

class C:
    def __init__(self, x: int | None):
        self.x = x

reveal_type(C().x)  # Should be `int | None`, is currently `Unknown | int | None`

We have pre-existing tests with TODO comments for this scenario. The goal of this issue it to get rid of these (there are more TODOs that would be resolved by this feature):

Part of: #14164